Github PR label automation

[Dr. Matthias St. Pierre]

> > Does it also check that the CI says that everything is OK?
>
> Do we want it to?  I assumed that Approval: done was not being applied
> unless tests past (but looking that's not always the case). Can we
> assume that something in "approval: ready to merge" but that failed CI
> won't get merged?  Otherwise I could add a CI check on the move to
> "ready to merge".

It does not check and I don't think it should attempt to do it. The only task of
this script should be to automatically promote the [approval: done] state to 
[approval: ready to merge] after the grace period has expired, because humans
tend to forget that. Anything beyond that, in particular an attempt to judge
whether the approval is valid or not, and whether a CI failure can be ignored or
not, should be left to humans.

Matthias